1. Field of the Invention
The present invention relates to a secondary air supply system for an internal combustion engine.
2. Description of the Prior Art
To purify hydrocarbons and carbon monoxide included in the exhaust gas from an internal combustion engine, so called secondary air is injected into an exhaust manifold or exhaust pipe of the engine. An air pump for pumping the secondary air is usually arranged in front of the engine and is driven by a pulley-belt assembly. More particularly, a pulley is coupled to the air pump and a crankshaft pulley is coupled to a crankshaft of the engine. A belt is wound around the pulleys and transmits rotation of the engine crankshaft to the air pump.
However, in such a pump driven by a pulley-belt assembly, it is often difficult to install an air pump and its pulley in front of the engine in the case of an engine also equipped with with a power steering device, an air conditioner, and a supercharger, because various pulleys for driving such elements are crowded in the same space.
Further, for an air pump driven by a pulley-belt assembly, a belt layout is required to be changed from a belt layout for an engine without air pump, and an auto-tensioner often needs to be provided for preventing the belt from slipping. The layout change and the addition of the tensioner greatly increase the cost.